1. Field of the Invention
The present invention relates generally to an induction system for an internal combustion engine wherein each combustion chamber has a plurality of inlet valves and more specifically to an arrangement wherein a flow control valve is located upstream of the inlet valves.
2. Description of the Prior Art
FIGS. 1 and 2 show an induction arrangement disclosed in Japanese Patent Application First Provisional Publication No. 58-48712(1983) published on Mar. 22, 1983. As shown, this arrangement is applied to an internal combustion engine wherein each cylinder has two inlet valves 1, 2 and wherein the induction ports 4, 6 which cooperate with the valves, are formed in a manner to be fluidly discrete from one and other. An induction manifold 8 is formed with essentially separate induction passages 10, 11 and includes a flow control valve 12 which is located near the downstream end thereof.
In order to promote a strong swirl during a low speed/low load operation the flow control valve 12 is mounted on a shaft 14 which is arranged essentially parallel with respect to the axis of the cylinder and formed with a cut-out 16. The flow control valve 12 is closed during low load/low speed engine operation, whereby the cut out 16 functions to guide the flow of incoming air in a manner such as shown in FIG. 1 into the combustion chamber via inlet valve 2 in a manner which produces a strong swirling flow pattern therein.
A fuel injector 18 is arranged to inject fuel into the intake port 6 in a manner to be entrained in the relatively high speed flow of air produced when the flow control valve 12 is closed.
When the engine enters high load operation the flow control valve 12 is fully opened and assumes the position shown in broken line thus permitting the maximum charging efficiency of the arrangement to be realized. Under these conditions the window or aperture 20 formed in the wall which separates the induction passages formed in the induction manifold is closed and the flow of air which passes from passage 10 to passage 11 during low load operation is terminated.
However, this arrangement, when applied to engines wherein multiple inlet and exhaust valves are use per cylinder and it is necessary to locate the spark plug in or near the center of the combustion chamber, encounters the drawback that despite the formation of a strong swirl the plug electrodes are not located in a good position to initiate flame propagation with a consequent reduction in the reliability with which a lean air-fuel mixture can be ignited.
Further, when the engine is operated under high load and the flow control valve 12 is moved to its full open position, as the fuel is injected exclusively into intake port 6, distribution thereof within the combustion chamber tends to be insufficient leading to a corresponding loss of combustion efficiency and anti-knock properties.